1. Field of the Invention
This invention relates to a one-way clutch allowing a rotating shaft to be rotated relatively to a cover when the rotating shaft is rotated in one direction and to be rotated integrally with the cover when it is rotated in the other direction.
2. Description of Related Art
FIG. 12 illustrates the entire configuration of a conventional one-way clutch, and FIG. 13 is a sectional view of the conventional one-way clutch. As illustrated in FIGS. 12 and 13, the one-way clutch includes a cover 1, a casing 2 incorporated inside the cover 1, a cap 3 for the cover 1, and a rotating shaft 4.
The cover 1 includes a cylinder 5 and a closing portion 6 closing one end of the cylinder 5. The cylinder 5 has an inside periphery on which a plurality of fitting heights 7 are formed. The closing portion 6 has a shaft hole 8 for supporting the rotating shaft 4.
The casing 2 has an outer peripheral face on which a plurality of fitting recesses 9 engage with the fitting heights 7 of the cover 1. The casing 2 is incorporated into the inside of the cover 1 by fitting between the fitting heights 7 and the fitting recesses 9. The casing 2 has a shaft hole 10 into which the rotating shaft 4 is inserted, and a plurality of needle holes 12 which are formed around the shaft hole 10 and into which needles 11 are inserted respectively.
Additionally, the casing 2 has a plurality of spring holes 14 formed for insertion of a spring member 13. The spring member 13 is provided for generating a spring force acting on the needles 11, and includes a plurality of springs 15 inserted into the respective spring holes 14, and an annular coupling portion 16 for coupling the plurality of springs 15.
The needle hole 12 and spring hole 14 have a shared are and are connected without a break. The needle hole 12 includes a sloped face 12a and a supporting face 12b opposite to the spring hole 14.
The sloped face 12a is inclined from the spring hole 14 toward the supporting face 12b. Specifically, the length between the sloped face 12a and the side face of the rotating shaft 4 is longer than the diameter of the needle 11 in the proximity of the spring hole 14, and shorter than the diameter of the needle 11 in the proximity of the supporting face 12b. That is, the sloped face 12a and the outer peripheral face of the rotating shaft 4 form a wedge-shaped clamping element.
In the needle hole 12 having the sloped face 12a as described above, the spring force of the spring member 13 acts on the needle 11 to allow it to come in contact with the rotating shaft 14.
The needle 11 and spring member 13, together with the needle hole 12 and spring hole 14 into which they are respectively inserted, form a clutch mechanism c.
The cap 3 closes the other end of the cylinder 5 of the cover 1, and has a shaft hole 17 for supporting the rotating shaft 4.
In the above configuration, the casing 2 is incorporated into the cover 1, and in turn the needles 11 and spring member 13 are incorporated into the casing 2. Then, the cap 3 is put over the cover 1 and casing 2. At this point, an annular height 3a formed on the cap 3 is fittingly snapped in an annular recess 1a formed on the cover 1.
In this way, after the cap 3 is set over the cover 1, the rotating shaft 4 is inserted so as to pass through the shaft hole 8 of the cover 1, the shaft hole 10 of the casing 2 and the shaft hole 17 of the cap 3.
Next the operation in the above configuration will be described.
The rotating shaft 4 is rotated in a direction represented by the arrow X in FIG. 3. Then, with the rotation of the rotating shaft 4 in the direction X, the rotating force and the spring force of the spring member 13 strongly push the needles 11 toward the supporting faces 12b of the needle holes 12. Strongly pushing the needles 11 toward the supporting faces 12b causes the needles 11 to be completely clamped in the respective wedge-shaped clamping elements formed by the sloped faces 12a and the outer peripheral face of the rotating shaft 4.
When the needles 11 are clamped in the clamping elements, each of the needles 11 increases the pressing force against the rotating shaft 4 to lock the rotation of the rotating shaft 4. If the rotating shaft 4 is locked, the rotating shaft 4 cannot rotate relative to the casing 2.
When the rotating shaft 4 is locked so as not to allow a rotation relative to the casing 2, if the rotating shaft 4 is further rotated in the direction X, the casing 2 is also rotated in the direction X with the rotation of the shaft 4.
Conversely, when the rotating shaft 4 is rotated in a direction represented by the arrow Y in FIG. 13, the needles 11 are pushed in the direction Y with the rotation of the shaft 4. When the needles 11 are pushed in the direction Y, the needles 11 flex the springs 15 while moving toward the spring holes 14. The needles 11 are then released from the clamping element because each needle hole 12 has a size in the proximity of the spring holes 14 larger than the diameter of the needle 11. In other words, there is no situation that the needles 11 are pressed toward the rotating shaft 4 to lock the relative rotation between the rotating shaft 4 and the casing 2. That is, the rotating shaft 4 is maintained in free rotation.
Thus, when the rotating shaft 4 is rotated in the direction Y, the rotating shaft 4 rotates relative to the casing 2. In other words, whenever the rotating shaft 4 is rotated in the direction Y, the casing 2 does not rotate with the rotation of the shaft 4.
Such a one-way clutch transfer to the casing 2 a rotative force generated when the rotating shaft 4 is rotated in one direction, and does not transfer to the casing 2 a rotative force generated when it is rotated in the other direction.
The conventional one-way clutch as described above needs high accuracy for the needle hole 12 and spring hole 14 serving as the clutch mechanism c especially. This is because, for example, if the clamping element of the needle hole 12 has a value higher than a set value, when the needle 11 is moved in the direction X, a longer time is required until the rotating shaft 4 is locked. In other words, a longer time is required from when the rotating shaft 4 is rotated until the rotating shaft 4 is locked and its rotation is transferred to the casing 2, resulting in impaired responsivity of the clutch function.
A possible simple means for maintaining accuracy of the needle hole 12 and the spring hole 14 is to use plastics for forming the casing 2 having the needle holes 12 and spring holes 14. Plastics can be used for molding, which provides a high accuracy.
However, plastics are sensitive to heat. Hence, when the casing 2 is molded of such plastics as described above, there is a problem of the impossibility of using the one-way clutch having such a plastics-made casing in high temperatures. Hence, this method is hardly ever employed.
Therefore, the casing 2 is formed of a sintered metal, because sintered metal is resistant to heat and additionally allows the forming of the spring hole 14 and the needle hole 12 with high accuracy. However, using a sintered metal requires a complicated molding process to provide a complicated configuration, and a high degree of technology, resulting in a high molding cost. This creates the problem that the entire one-way clutch is costly.
Using a sintered metal produces another problem of a low strength. Specifically, as explained earlier, when the rotating shaft 4 is rotated in the direction X, the needle 11 is pressed against the sloped face 12a with a strong force. In addition, when the relative rotation between the rotating shaft 4 and the casing 2 is locked and this lock state is maintained, the needle 11, especially, is pressed against the sloped face 12a of the needle hole 12 with a very strong force. For resisting the pressing force, the casing 2 needs a high strength.
Therefore, there is another method devised for forming the needle hole 12 and spring hole 14 with high accuracy using a metal as explained below. This is a method of forming the needle holes 12 and spring holes 14 on a metal plate member through a press process, and then laminating a plurality of the resulting plate members.
In an additional possible step, after completion of laminating the metal plate members, the laminated plate members are press-fitted for maintaining the lamination. FIG. 14 illustrates a plate member 18 used for a core of a motor.
The plate member 18 includes an annular member 19, branch-shaped portions 20 which are provided to the annular member 19 and on which a leading wire is wound, and dot-shaped press-fit elements 21 formed in the respective portions 20. The press-fit element 21 is formed through a stamping process, in which a recess is formed on one surface of the plate member 18 and a height on the other surface.
The above plate members 18 are laminated by means of press-fitting the heights of the press-fit elements 21 of each plate member 18 into the corresponding recesses of the press-fit elements 21 of the plate member above, in order to prevent separating of the laminated plate members 18.
However, if the method employed for the core of the motor shown in FIG. 14 is directly adapted to the one-way clutch, the pressing force of the needles separates the laminated members. Further, if a large number of dot-shaped press-fit elements are formed in the plate member in order to sufficiently ensure a holding force generated by the press-fit elements, it produces a problem of an increased size of the entire one-way clutch.